Sydenham's chorea is the only accepted immune-mediated central nervous system manifestation of group A beta hemolytic streptococcal (GABHS) infection. Several lines of evidence now suggest that there may be a spectrum of post-GABHS immune- mediated neurobehavioral sequelae termed "Pediatric Autoimmune Neuropsychiatric Disorders after Streptococcal Infection (PANDAS)". Tics, including Tourette's syndrome (TS), and obsessive-compulsive disorder (OCD) have been reported as the characteristic features of PANDAS. Proposed is a multicenter prospective case control cohort study involving 40 cases of PANDAS and 40 matched controls with TS and/or OCD but without evidence of PANDAS. All subjects will undergo intensive clinical and laboratory prospective observation for 24 months to determine whether antecedent GABHS infection is: 1) temporally associated with exacerbations of PANDAS, 2) specifically associated with exacerbations of tics and OCD, and 3) a specific trigger for exacerbations of PANDAS. All determinations of case/control status, GABHS infection and clinical exacerbation will be determined independently by blinded review in order to limit selection and clinical biases. Establishing a post-infectious etiology for PANDAS would dramatically change our understanding of the causes of TS and OCD, alter our therapeutic approach and may have a critical public health implication of preventing potentially fatal rheumatic cardiac sequelae in affected children. Disproving the PANDAS hypothesis would prevent the use of expensive and potentially dangerous therapies (e.g., plasma exchange, immune globulin, antibiotics) that have been proposed for PANDAS patients.